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The development of renewable energy is becoming an increasingly important objective for a growing number of countries around the world for several reasons. Renewable energy has an important role to play in reducing greenhouse gas emissions (particularly carbon dioxide, CO2). Increasing the share of renewable energy in the energy balance enhances sustainability. It also helps to improve the security of energy supply by reducing countries’ dependence on imported energy sources. Fossil fuels are non-renewable, that is, they draw on finite resources that will eventually dwindle, becoming too expensive or too environmentally damaging to extract. In contrast, renewable energy resources, such as wind and solar energy, are constantly replenished and will never run out.
Most renewable energy comes from the sun, either directly or indirectly. The sun’s heat and light, or solar energy, provides an abundant source of energy that can be harnessed in many ways. It can be used for heating and lighting homes and other buildings, for generating electricity, for water heating, solar cooling, and a variety of commercial and industrial uses. Several technologies have been developed to take advantage of solar energy, including concentrating solar power systems, passive solar heating and day lighting, photovoltaic systems, solar water heaters, solar process heat and space heating and cooling. Solar power can be used in large-scale applications and in smaller systems for the home. Humans have been harnessing the wind’s energy for hundreds of years. From old Holland to farms in the United States, windmills have been used for pumping water or grinding grain. Today, the windmill’s modern equivalent, the wind turbine, uses the wind’s energy to generate electricity. Wind turbines can be used as stand-alone applications, or they can be connected to a utility power grid or even combined with a photovoltaic (solar cell) system.
Along with the rain and snow, sunlight causes plants to grow. The organic matter that makes up those plants is known as biomass. Biomass can be used to produce electricity, transportation fuels, or chemicals. The use of biomass for any of these purposes is called biomass energy or “bioenergy”.
Hydrogen is the most abundant element on the Earth. It literally grows on trees and falls with the rain, as it is found in many organic compounds, and is one of the two chemical constituents of water. When isolated from these compounds, hydrogen gas can be burned to produce energy that can be used directly or converted into electricity, emitting only water vapour. Fuel cells that electrochemically combine hydrogen and oxygen to produce electricity and heat offer the promise of more sustainable energy generation, because they can generate energy without emitting any of the gases responsible for global warming. One vision for a more sustainable future is the idea of the “hydrogen economy,” in which hydrogen fills vehicle fuel tanks instead of gasoline, is piped to homes for heating and cooking instead of natural gas, and is used to generate electricity onsite instead of sending electricity through transmission lines.
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